The present invention relates to a capacitor for semiconductor memory device and a method of manufacturing the same, and more particularly to a capacitor for semiconductor memory device capable of increasing the storage capacitance as well as preventing leakage current and a method of manufacturing the same.
As the number of memory cells composing DRAM semiconductor device has been recently increased, occupancy area of each memory cell is gradually decreased. Meanwhile, capacitors formed in the respective memory cells require a sufficient capacitance for precise reading out of storage data. Accordingly, the current DRAM semiconductor device requires memory cells in which capacitors having larger capacitance as well as occupying small area are formed. The capacitance of a capacitor can be increased by using an insulator having high dielectric constant as a dielectric layer, or by enlarging the surface area of a lower electrode. In a highly integrated DRAM semiconductor device, a Ta2O5 layer having a higher dielectric constant than that of the nitride-oxide(NO) is now used as a dielectric, thereby forming a lower electrode of a 3-Dimentional structure.
FIG. 1 is a cross-sectional view showing a capacitor for a conventional semiconductor memory device. Referring to FIG. 1, a gate electrode 13 including a gate insulating layer 12 at a lower portion thereof is formed according to a known technique on the upper part of a semiconductor substrate 10 which a field oxide layer 11 is formed at a selected portion thereof. A junction region 14 is formed on the semiconductor substrate 10 at both sides of the gate electrode 13, thereby forming an MOS transistor. A first interlayer insulating layer 16 and a second interlayer insulating layer 18 are formed on the upper part of the semiconductor substrate 10 which the MOS transistor is formed therein. A storage node contact hole h is formed inside the first and the second interlayer insulating layers 16,18 so that the junction region 14 is exposed. A cylinder type lower electrode 20 is formed according to a known method, inside the storage node contact hole h so as to be in contact with the exposed junction region 14. A HSG(hemi-spherical grain) layer 21 is formed on a surface of a lower electrode 20 to increase the surface area of the lower electrode 20 more. A tantalum oxide layer 23 is formed on the surface of the HSG layer 21. Afterwards, the Ta2O5 layer 23 is deposited on the upper part of the lower electrode 20 including the HSG layer 21 by using an organic metal precursor such as Ta(OC2H5)5. Afterwards, the Ta2O5 layer 23 is thermal-treated at a selected temperature so as to crystallize. An upper electrode 25 is formed of a polysilicon layer or a metal layer doped on the upper part of the Ta2O5 layer 23.
However, a difference in the composition rate of Ta and O is generated since the Ta2O5 layer 23 generally has unstable stoichiometry. As a result, substitutional Ta atoms, i.e. vacancy atoms are generated in a thin film. Since those vacancy atoms are oxygen vacancies, leakage current is generated.
Now, a process for oxidizing the Ta2O5 layer has been additionally performed to remove the substitutional Ta atoms therein. However, when performing this oxidizing process, an oxide reaction of the Ta2O5 layer with the upper and the lower electrodes actively progresses. As a result, an oxide layer having a low dielectric constant is formed on the interface between the Ta2O5 layer and the lower electrode or the upper electrode, thereby deteriorating the homogeneity of the interface and increasing the thickness of an effective oxide layer as well as manufacturing process steps.
Moreover, since the Ta2O5 layer is formed by a reaction between an organic tantalum precursor containing carbon components and oxygen, reaction impurities such as carbon atoms (C), carbon compounds(CH4, C2H4), and H2O remain therein after the deposition process. These reaction by-products cause leakage current and deteriorate the dielectric strength of the Ta2O5 layer.
To remove these reaction by-products, the Ta2O5 layer has been conventionally deposited more than 2 layers, at least. And, after each deposition step, a plasma treatment or UVxe2x80x94O3 process has been additionally performed to remove reaction by-products inside the Ta2O5 layer. However, the above method has a demerit of increase in the number of the processes.
Accordingly, it is one object of the present invention to provide a capacitor for a semiconductor memory device with a dielectric layer having low leakage current and high dielectric constant.
Furthermore, the other object of the present invention is to provide a method of manufacturing a capacitor for a semiconductor memory device capable of simplifying manufacturing process thereof.
To achieve the foregoing objectives, a capacitor for a semiconductor memory device of the present invention according to one aspect includes: a lower electrode; a dielectric layer formed on the lower electrode; and an upper electrode formed on the upper part of the dielectric layer, wherein the dielectric layer is a (TaO)1-x(TiO)N layer.
Further, the present invention according to another aspect provides a method of manufacturing a capacitor of a semiconductor memory device including the steps of: forming a lower electrode on the semiconductor substrate; depositing a (TaO)1-x(TiO)N layer as a dielectric layer on the upper part of the lower electrode; and forming an upper electrode on the upper part of the (TaO)1-x(TiO)N layer.
And, the present invention according to still another aspect provides a method of manufacturing a capacitor of a semiconductor memory device including the steps of: forming a lower electrode on the semiconductor substrate; surface-treating to prevent a natural oxide layer from generating on the surface of the lower electrode; depositing the (TaO)1-x(TiO)N layer as a dielectric on the upper part of the lower electrode; diffusing and simultaneously crystallizing impurities inside the (TaO)1-x(TiO)N layer; and forming an upper electrode on the upper part of the (TaO)1-x(TiO)N layer, wherein the (TaO)1-x(TiO)N layer is formed by a surface chemical reaction of Ta chemical, Ti chemical vapor, NH3 gas and O2 gas in an LPCVD chamber maintaining a temperature of 300 to 600xc2x0 C.